The present invention relates to a simple, field-installable, removable filter/dryer, and more particularly, to a filter/dryer housing used in vapor compression air conditioners, heat pumps, refrigerators and the like which can be attached into the liquid line or vapor line of the system.
Filter/dryers are used to clean refrigerant by removing particles, moisture, and/or acid from the refrigerant by mechanical filtration, adsorption, absorption, or other mechanical and chemical mechanisms. The function of these devices could be referred to as “cleaning” the refrigerant.
The presence of acid in the refrigerant of vapor compression refrigerators, heat pumps, and air conditioners severely shortens the life of both the compressor and the refrigerant. The presence of moisture in the refrigerant of vapor compression refrigerators, heat pumps, and air conditioners leads to the formation of ice crystals in the throttling device, thereby restricting the flow of refrigerant and decreasing capacity. The presence of water in a system also accelerates the formation of acids in the system. Installing a filter/dryer in the system to adsorb moisture and acid (as well as filtering out solid particles) is a common maintenance procedure. These filters are typically located in the liquid line upstream of the expansion device, but are also located in the suction line to trap acid returning to the compressor when a new compressor has been installed after a compressor burn-out.
Aside from the situation where a major repair is being performed on the system (requiring the recovery of the refrigerant and replacement of critical components such as the compressor, evaporator, or condenser), the labor involved in changing an in-line filter/dryer is too cost-prohibitive on smaller, less expensive systems especially when the capacity of the remaining filter/dryer is unknown. Likewise, on systems that do not have a filter/dryer, which are usually smaller, less sophisticated and less expensive systems, the repeated labor costs associated with repeatedly installing an in-line filter/dryer typically keep refrigeration/air conditioning service technicians from ever installing or even changing an existing filter/dryer.
Therefore, if a filter/dryer is installed in a lower-cost system, it is rarely changed. When only one such a filter/dryer is located in a system, it is typically located in the liquid line directly upstream of the expansion device. When a second filter/dryer is utilized for acid control, typically after a burnout, this second filter/dryer is located in the compressor suction line, upstream of the compressor inlet. In either case, the desiccant, adsorption media and filter medium used in these refrigerant filter/dryers is well known in the art as discussed, for example, in U.S. Pat. Nos. 4,665,050; 5,114,584; 5,384,047; 5,364,540; and 5,440,898. This adsorption media is typically located either in a sealed replaceable disposable filter/dryer assembly or in a “replaceable core” filter/dryer.
In the replaceable core configuration, the filter/dryer media is usually formed into a semi-rigid porous structure that is placed into the reusable, refillable replaceable core filter/dryer housing. These replaceable core filter/dryers have been available commercially for many years as seen in the March 1989Sporlan “Catch All” Filter Dryer Bulletin No. 40-10. These removable housing designs are also discussed in U.S. Pat. Nos. 3,286,838; 4,581,903; and 4,683,057, which discuss methods for sealing the filter/dryer core to the interior of the housing so as to prevent by-pass leakage around the filter.
Likewise, the sealed disposable filter/dryer assemblies are also well known in the prior art and are also described in the aforementioned March 1989 Sporlan “Catch All” Filter Dryer Bulletin No. 40-10. In these disposable filter/dryer devices, the filter/dryer medium is either a rigid core like the replaceable core filter/dryer or a loose fill of desiccant/adsorbent material held within the sealed disposable filter housing. There are many different approaches in the design and construction of these disposable replaceable canisters, as seen, for example, in U.S. Pat. Nos. 4,255,940; 4,177,145; 5,240,483; 5,910,165; 5,837,039; 5,425,250; 5,375,327; 5,245,842; 5,215,660; 5,814,136; and 5,522,204, all of which use a loose fill adsorbent material contained within a porous package. This filter/dryer desiccant (adsorbent) material is sealed within the filter/dryer housing. There are also disposable canisters described in U.S. Pat. No. 5,440,898 which utilize a rigid filter/dryer core molded from a permeable matrix of desiccant particles, a binder, and reinforcing fibers.
U.S. Pat. No. 2,017,350 discloses a foot valve and strainer organized to permit co-operation therebetween when in normal use and removal thereof from the device by a simple operation when cleaning or replacement is necessary. While the known replaceable core filter/dryers employ the concept of a removable housing and U.S. Pat. No. 2,017,350 discusses a pressure-actuated foot valve, the prior art did not recognize and certainly did not discuss the need for a method for mechanically sealing (isolating) both the inlet and outlet to the filter/dryer assembly automatically as a direct result of the action of removing the filter/dryer housing, and automatically opening both the inlet and outlet to the filter/dryer assembly automatically as a direct result of the action of attaching the filter cover into the base.
It was also well known in the art prior to the present invention to use a cylindrical filter or filter/dryer element with a cylindrical inner volume for receiving the fluid which is passed through the porous filter media and to fasten and prevent short-circuiting of the fluid from around the ends of the filtering structure within the housing. For example, the aforementioned U.S. Pat. No. 2,017,350 discusses one such fastening method using a rod extending axially through the strainer, whereas U.S. Pat. No. 3,286,838 discusses external springs and U.S. Pat. No. 4,255,940 uses an external spring-and-cap arrangement.
U.S. Pat. No. 5,211,024 discloses a refrigerant filtration system with a filter change indication. A flow meter monitors the volumetric flow of refrigerant through the filter to determine when the filter should be changed as a function of the mass of refrigerant which has been pumped through the filter. This meter does not, however, determine the remaining capacity of the filter. Rather, it simply indicates the need to change the filter/dryer when a particular volume of refrigerant has passed therethrough. Because the remaining drying capacity of the filter/dryer is a direct function of the moisture and acid content of the refrigerant that has passed through and not merely the total mass of refrigerant, this known method is of questionable value, and in fact a simple timer (hour meter) would be of equal utility and result in reduced cost.
Finally, U.S. Pat. No. 5,915,402 discloses an isolation valve including an integral pair of ball valves close coupled by a custom union for disconnecting and replacing the charge refrigeration components. As seen in FIG. 6 of that patent, two such valves can be used with any refrigeration component, including a filter/dryer to allow the component to be removed from the system without removing the entire refrigerant charge of the system. This device, although intended to be convenient, is also more complex than simply using two common refrigeration shut-off (isolation) valves and is essentially similar to using any conventional shut-off valve on both the inlet and outlet side of the component to be removed. Furthermore, this approach does not allow the system to operate when the filter or other refrigeration component located between the two valves has been removed.